Search The Blog

Follow me on Twitter

Q: What does it mean when you say a pond must “cycle” before adding fish?

Sherry – Raleigh, NC

A: The term “cycle” refers to the nitrogen cycle – and it’s an important process to understand if you plan to keep fish in your pond. The nitrogen cycle provides the biological filtration in the water, which keeps the water free from toxic compounds created by decaying organic matter. The process is a complicated one, so here are the basics.

Nitrogen Cycle 101

Before we discuss cycling a new pond, let’s dive into how the nitrogen cycle looks in an established, mature pond. As organic material – like uneaten food, dead plant matter and fish waste – decay, the bacteria that break it down release ammonia, which is toxic to living organisms. One particular microorganism called nitrosomonas, however, loves ammonia. It feeds on ammonia and oxygen, and releases a chemical called nitrite.

Nitrites are also dangerous to fish and aquatic critters, and so another group of microorganisms – nitrobacter – enters the nitrogen cycle picture. These bacteria transform nitrites into relatively harmless nitrates, which are then absorbed by algae and plants or reduced by water changes.

New Pond, New Bacteria

A new pond doesn’t have healthy populations of nitrosomonas and nitrobacter yet, and so the pond must be “cycled.” This refers to establishing and maturing your pond’s biological filtration system so that it’s able to turn ammonia into nitrates. To do so, you need to start the process with an ammonia source (a few hardy fish) and seed the pond with these beneficial bacteria, which can be found in Pond Logic® Seasonal Defense® and in Microbe-Lift® PL Gel.

Nurturing Nitrosomonas

In the early spring when established ponds are waking up after a long winter, a similar cycling process will take place. Some nitrosomonas and nitrobacter will survive in your filtration media and gravel and begin to colonize, but it’s a good idea to give them a boost. Pond Logic® Seasonal Defense® is formulated for use in cooler temperatures – making it perfect for early spring applications. Since those microorganisms live in your filtration media, avoid washing it when you’re doing your spring cleaning.

Cycled and Ready for Fish

The cycling process can take four to six weeks, though in the warmer spring and summer this time may be reduced. Keep an eye on your ammonia, nitrite and nitrate levels with a test kit, like our API® Pond Master Test Kit. Once it indicates that nitrates are present, your pond is considered cycled. Add only a few fish at a time to prevent ammonia levels from spiking again.

Keep in mind that this ammonia-nitrite-nitrate cycle is always occurring, so test your pond regularly to ensure the health and wellbeing of your finned friends.